1. Field of the Invention
The present invention relates to information processing adapted for recording or reproducing a transport stream signal in which plural programs are multiplexed on time-division basis.
2. Related Background Art
For the broadcasting system of the next generation, the digital broadcasting employing MPEG (moving picture experts group) 2 system, in which plural programs are transmitted by multiplexing on time-division basis, is attracting attention.
In the following there will be explained the general time-division multiplexing system based on the MPEG2 system.
For example in the time-division system for video data, the DTS (decoding time stamp) for timing of fetching data from the decoder buffer at the decoder side and the PTS (presentation time stamp) for timing of displaying the data are inserted into the top of each picture. More specifically, each picture data of variable length is packetized into a packet called PES (packetized elementary stream), and PTS/DTS are inserted in the header of PES whereby the video/audio data can be synchronized.
The PTS/DTS are in practice composed of values of a counter functioning with the system clock signal (27 MHz) of the encoder. Consequently, there may be resulted in overflow/underflow of the buffer unless this system clock is reproduced also in the decoder side. Consequently, at the level of packetizing into 188 bytes, the counts of the system clock are periodically inserted as PCR (program clock reference). In the decoder, the PCR is detected and the system clock of the encoder is reproduced through a VCO (voltage-controlled oscillator) of 27 MHz and a PLL (phase locked loop). When plural programs are multiplexed, the PCR is inserted in the packet of each program.
FIG. 1 shows the configuration of a transport packet based on MPEG2.
The transport packet has a fixed length of 188 bytes. The header portion of the transport packet contains identification information indicating the content of the packet data, whereby a packet required for the reproduction of the desired program can be selected and decoded.
As shown in FIG. 1, the transport packet is provided, at the start of the packet, with a header, which is followed by payload (information).
The header is composed of sync data of 8 bytes, a transport error indicator indicating the presence or absence of error in the packet, a payload unit start indicator indicating the start of the payload unit, a transport priority indicating the importance of the packet, a packet identification (PID) indicating the attribute of individual stream of the packet, a transport scramble control indicating the presence or absence of scramble of the payload and the kind thereof, an adaptation field control indicating the presence or absence of adaptation field, a cyclic counter for detecting whether the packet has been partially discarded on the way, and an adaptation field that can contain additional information on the individual stream and stuffing bytes.
The adaptation field contains an adaptation field length indicating the length of the adaptation field, a discontinuity indicator indicating that the system clock is reset and renewed as a new content, a random access indicator indicating the entry point of random access, a priority stream elementary indicator indicating that an importance portion exists in the payload, and an optional field.
The optional field contains a PCR, an OPCR, a splice countdown, a transport private data length, transport private data, an adaptational field extension length, and an optional field. The PCR is a time stamp for setting and calibrating a time reference value in the MPEG system decoding. The system clock (27 MHz) is reproduced from the PCR by PLL, and the time axis information of the packet is retained as the reference of timing of the subsequent decoding process.
There are presently being developed recording/reproducing apparatus for recording and reproducing the above-described TS.
Among such apparatus, there is being developed a recording/reproducing apparatus having so-called delayed reproducing function, in which, while the digital broadcast program is recorded, the already recorded content is reproduced.
Such recording/reproducing apparatus is capable of recording a currently broadcast program and at the same time allows the user to reproduce and observe such program with a certain delay in time. For example, in case a live sport program is extended, the user can continue to observe the sport program, while recording for example a drama program, broadcast at the same time in another channel, on a recording medium, and can reproduce the recorded program from the beginning after the sport program is terminated, whereby the user can observe the currently broadcast program with the delay of an arbitrary time.
Also the recorded program can be given a special reproducing function such as slow reproduction or search reproduction, so that the currently broadcast program can be displayed as if the currently broadcast program could be reproduced with such special reproduction.
In the recording/reproducing apparatus capable of recording and reproducing by selecting a desired transport stream (TS) only from the TS containing plural programs by time-division multiplexing in order to attain the above-described functions, the data readout speed from the recording medium is controlled at the reproduction, after the demultiplexer, in order to maintain such a bit rate as not causing data underflow or overflow.
As a method of such recording and reproduction, in order to match the decoding rate with the rate of the reproduced bit stream, there is known a method of adding a time stamp on each transport stream at the recording operation and, at the reproduction, controlling the readout of the bit stream so as to match such time stamp.
However, such method has been associated with a drawback of an increased load for controlling the data readout rate in order to maintain the bit rate. Also there may be recorded all the entered TS to avoid the increase of load, but the recording capacity becomes unnecessarily large in order to record the programs other than the desired one.
Further, there is resulted in a drawback that the amount of recorded information becomes large in case the time stamp is attached to every recorded transport stream.